Magnetic reproducing head having a structure to inhibit electrostatic discharge damage to a recording tape

ABSTRACT

A head substrate and a protective substrate are formed of an electrostatic-discharge resistant conductive material having an electrical resistivity of 10 2  to 10 10  Ωcm. These substrates are electrically connected to a base metal through the use of conductive paste and are set to a ground potential via the base metal and a rotating drum. This suppresses a discharge current flowing through an MR element when an electrostatically charged substance touches or approaches a magnetic reproducing head, a terminal, a conducting wire, etc. to generate an electrostatic discharge. The magnetic reproducing head including an MR element and the like is prevented against an electrostatic discharge damage. It is possible to provide the magnetic reproducing head, a head drum apparatus, and a magnetic recording-reproducing apparatus which can highly effectively prevent an electrostatic discharge damage.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application No.P2001-311911 filed Oct. 9, 2001, which application is incorporatedherein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a head drum apparatus for writing andreading signals on magnetic tape and a magnetic recording-reproducingapparatus having the head drum apparatus. More specifically, the presentinvention relates to a helical scanning magnetic reproducing head usingan MR head, a head drum apparatus, and a magnetic recording-reproducingapparatus having the head drum apparatus.

2. Description of Related Art

In recent years, as the amount of information to be handled increases,there is an increasing need for further improving recording densitiesfor a magnetic recording-reproducing apparatus that records andreproduces data on magnetic tape. It is absolutely necessary to use anMR (Magneto Resistive) head instead of a conventional inductive head asa magnetic head for reading signals. The MR head is a magnetic head thatreads a signal recorded on a magnetic recording medium using the magnetoresistive effect of an MR element. The MR head can provide highsensitivity of signal detection and large reproduction output.Accordingly, the MR head can easily reduce a recording track width onthe magnetic tape, increase the recording density in a linear direction,and provide high-density recording and reproduction.

Generally, the MR head is characterized by susceptibility toelectrostatic discharge and heat attack compared to inductive heads.FIG. 4 shows results of measuring ESD (Electrostatic Discharge)breakdown voltages at MR heads. FIG. 4A shows the measurement result ofan AMR (Anisotropic Magneto Resistive) head. FIG. 4B shows themeasurement result of a GMR (Giant Magneto Resistive) head.

With respect to measured values in FIG. 4, an HBM (Human Body Model) isused to measure ESD breakdown voltages. FIG. 4 shows the relationshipbetween a voltage applied to the device and a resistance when a 100 pFcapacitor is charged and then discharged with the resistance of 1.5 kΩ.According to the measurements, the AMR is supplied with an ESD breakdownvoltage of approximately 230 to 240 V. The GMR is supplied with an ESDbreakdown voltage of approximately 30 to 40 V.

Under normal conditions, friction, contact, induction, or the likeeasily generates a charged voltage of several kilovolts or more on aninsulator such as plastic, nylon, vinyl, etc. For example, ahigh-resistance synthetic resin material is often used to form aconventional cassette case for taking up and storing magnetic tape. Suchcassette case is easily electrostatically charged while a user handlesit, for example, due to friction with a packaging material made ofartificial fiber, friction with parts when the cassette case is loadedinto the magnetic recording-reproducing apparatus, etc.

An ABS resin is one of synthetic resin materials used for cassettecases. For example, an ABS resin with the surface resistance ofapproximately 10¹⁶Ω/sq generates a charged voltage of 1.5 to 2 kV ormore. It takes three minutes or more to halve the charged voltage. Thischarged voltage value far exceeds the MR head's withstand voltage. Inaddition, since the time to halve the charged voltage is long, thestatic electrification, once charged, hardly attenuates. If the magnetictape in the electrostatically charged cassette case touches the MR head,a large amount of current flows through the MR head, possibly causing anelectrostatic discharge damage.

A conventional MR head uses a head substrate comprising an MR elementsandwiched between magnetic shielding films or insulating films. Theprotective substrate uses a conductive material such as Al₂O₃—TiC withthe electrical resistivity of approximately 2×10−3 Ωcm. The magnetichead is electrically connected to the drum apparatus so that the headsubstrate and the protective substrate become the ground potential. Whenthe electrostatically charged magnetic tape touches the MR head, theelectric charge does not flow through the MR element, but through thehead substrate and the protective substrate for discharge.

When the head substrate and the protective substrate are made conductiveas mentioned above, however, a high voltage is applied to the MR elementdue to approach, contact, etc. of a charged substance from the outside.When the electrostatic change is discharged between these substrates, avery large discharge current is generated because the substrates have alow electric resistance. Accordingly, the discharge current flowsthrough the MR element to cause an electrostatic discharge damage.

FIG. 5 schematically shows a discharge on the conventional MR head.

FIG. 5 shows a structure example of an MR head 50 against a magnetictape's contact surface. The MR head 50 is structured to arrange an MRelement 50 c, and a pair of shielding films 50 d and 50 e made of a softmagnetic material between a head substrate 50 a and a protectivesubstrate 50 b that are both conductive. Insulating films 50 f and 50 gare formed between a head substrate 50 a and a protective substrate 50 band between shielding films 50 d and 50 e. The MR element 50 c is formedbetween the shielding films 50 d and 50 e via insulating films 50 h and50 i to constitute a reproducing magnetic head section. The MR element50 c is connected to a power supply terminal (not shown) through aconducting wire etc. The MR element 50 c is powered from the powersupply terminal to read data recorded on the magnetic tape.

The MR head 50 is fixed on a base metal (not shown). The base metal isfixed on a rotating drum (not shown) to mount the MR head 50 thereon.The base metal is made of conductive metal. The head substrate 50 a andthe protective substrate 50 b are electrically connected to the basemetal through conductive paste, for example. The base metal is fixed onthe rotating drum with a metal fixing screw or the like, for example.The rotating drum is connected to the ground in the apparatus to allowthe head substrate 50 a and the protective substrate 50 b to be equal tothe ground potential. Accordingly, when the electrostatically chargedmagnetic tape touches or approaches the head, for example, the magnetictape is discharged through the head substrate 50 a and the protectivesubstrate 50 b.

Concerning the MR head 50, a charged substance such as rubbed artificialfiber may touch or approach the power terminal during a production lineprocess, for example. In such case, the electric charge moves to thepower supply terminal from the charged substance, increasing the voltageof the MR element 50 c. At this time, the electric field concentrates onthe shielding film 50 d, and then on the head substrate 50 a from the MRelement 50 c touching the magnetic tape's contact surface, thusincreasing an electric field strength. Since the insulating films 50 fthrough 50 i are thin on the magnetic tape's contact surface, adielectric breakdown occurs on these films. A discharge current flowsinto the head substrate 50 a from the MR element 50 c via the shieldingfilm 50 d.

Since the head substrate 50 a has a low electric resistance at thistime, an excessive current flows into the head substrate 50 a from theMR element 50 c. Consequently, discharged traces 51 a, 51 b, 51 c, and51 d are formed at discharged locations on the MR element 50 c, theshielding film 50 d, and the head substrate 50 a.

Further, when the charged substance touches or approaches the magnetictape contact surface of the MR head 50, an electric discharge is appliedto the head substrate 50 a or the protective substrate 50 b to cause anelectrostatic discharge damage. FIG. 6 is a graph showing an electriccurrent waveform when the conventional MR head 50 is subject to theexperiment on discharging.

FIG. 6 shows currents generated when a voltage-applied probe is movedclose to the magnetic tape contact surface of the MR head 50 for adischarge. The applied direct-current voltage is up to 3 kV. As seenfrom the graph, it is possible that an absolute value for the currentexceeds 1 A during a discharge. The MR element 50 c is easily subject tomeltdown and the like. In addition, a discharge current destroys theshielding films 50 d and 50 e, the head substrate 50 a, and theprotective substrate 50 b.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the foregoing.It is therefore an object of the present invention to provide a magneticreproducing head and a head drum apparatus capable of preventing anelectrostatic discharge damage from occurring at an MR head for magnetictape reproduction when an electrostatically charged substance touches orapproaches the MR head.

It is another object of the present invention to provide a magneticrecording-reproducing apparatus capable of preventing an electrostaticdischarge damage from occurring at an MR head for magnetic tapereproduction when an electrostatically charged substance touches orapproaches the MR head.

To solve the above-mentioned problems, one aspect of the presentinvention resides in a magnetic reproducing head and a head drumapparatus to write or read a signal from magnetic tape, characterized bycomprising: a rotating drum having conductivity to be a groundpotential, wherein the magnetic tape is helically wound around anexternal surface of the rotating drum; a base metal which is fixedinside the rotating drum and is electrically connected to the rotatingdrum; and a magnetic head section fixed to the base metal, wherein amagneto resistive effect element to read a recording signal in contactwith the magnetic tape is used for a head element section comprisingfirst and second insulating films provided between a pair of magneticshielding films; the head element section is structured to be providedbetween a head substrate and a protective substrate electricallyconnected to the base metal via third and fourth insulating films; andeither or both of the head substrate and the protective substrate aregiven an electrical resistivity of 10² to 10¹⁰ Ωcm.

The magnetic reproducing head and the head drum apparatus use a materialhaving the electrical resistivity of 10² to 10¹⁰ Ωcm for either or bothof the head substrate and the protective substrate. These substrates areelectrically connected to the base metal to be equal to a groundpotential via the base metal and the rotating drum. When anelectrostatically charged substance touches or approaches the magnetichead section to discharge electrostatic change, it is possible tosuppress a discharge current flowing through the head element. Thismakes it possible to prevent an electrostatic discharge damage in themagnetic head section such as the head element and the like.

Another aspect of the present invention resides in a magneticrecording-reproducing apparatus to record and reproduce a signal usingmagnetic tape, characterized by comprising: a rotating drum havingconductivity to be a ground potential, wherein the magnetic tape ishelically wound around an external surface of the rotating drum; a basemetal which is fixed inside the rotating drum and is electricallyconnected to the rotating drum; and a magnetic head section fixed to thebase metal, wherein a magneto resistive effect element to read arecording signal in contact with the magnetic tape is used for a headelement section comprising first and second insulating films providedbetween a pair of magnetic shielding films; the head element section isstructured to be provided between a head substrate and a protectivesubstrate electrically connected to the base metal via third and fourthinsulating films; and either or both of the head substrate and theprotective substrate are given an electrical resistivity of 10² to 10¹⁰Ωcm.

The magnetic recording-reproducing apparatus uses a material having theelectrical resistivity of 10² to 10¹⁰ Ωcm for either or both of the headsubstrate and the protective substrate. These substrates areelectrically connected to the base metal to be equal to a groundpotential via the base metal and the rotating drum. When anelectrostatically charged substance touches or approaches the magnetichead section to discharge electrostatic change, it is possible tosuppress a discharge current flowing through the head element. Thismakes it possible to prevent an electrostatic discharge damage in themagnetic head section such as the head element and the like.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration example of a magneticreproducing head;

FIG. 2 is a perspective view showing a configuration example of a headdrum apparatus according to the present invention;

FIG. 3 is a side view showing a configuration example of the magneticreproducing head;

FIGS. 4A and 4B show results of measuring ESD breakdown voltages at MRheads;

FIG. 5 schematically shows a discharge on a conventional MR head; and

FIG. 6 is a graph showing an electric current waveform when theconventional MR head is subject to the experiment on discharging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in furtherdetail with reference to the accompanying drawings.

FIG. 2 is a perspective view showing a configuration example of a headdrum apparatus according to the present invention.

A head drum apparatus 1 as shown in FIG. 1 writes and reads data onmagnetic tape 2 according to the helical scanning system. For example,the head drum apparatus 1 is used for magnetic recording-reproducingapparatuses including a VTR (video tape recorder) and a video camerawith VTR for recording and reproducing video and audio signals, a datastorage apparatus for computers, etc.

The cylindrical head drum apparatus 1 has a smooth external surface as awhole. The head drum apparatus 1 comprises a rotating drum 11, arotating shaft for the rotating drum 11, and a fixed drum 12 fixed onthe rotating shaft. The external surface of the fixed drum 12 isprovided with a lead 12 a for guiding magnetic tape 2. Along the lead 12a, the magnetic tape 2 travels by being helically wound around theexternal surface of the head drum apparatus 1. The rotating drum 11 isprovided with a magnetic reproducing head section 13 for detecting asignal recorded on the magnetic tape 2 and a magnetic recording head(not shown) for writing a signal.

The magnetic reproducing head section 13 is an MR head using a magnetoresistive effect (MR) element as a head element. The magneticreproducing head section 13 is configured to slightly protrude from theexternal surface of the rotating drum 11 and touch the magnetic tape 2.The magnetic reproducing head section 13 slantwise scans the magnetictape 2 in accordance with rotation of the rotating drum 11. The magneticreproducing head section 13 detects changes in MR element's resistancevalues in response to a recorded signal to read the signal recorded onthe magnetic tape 2. The magnetic recording head is a so-calledinductive magnetic head apparatus, e.g., comprising a coil wound arounda magnetic core having a magnetic gap. Though not shown in FIG. 2, therotating drum 11 is normally provided with a plurality of the magneticreproducing heads 13 and the magnetic recording heads.

A cassette case containing the magnetic tape 2 is loaded into themagnetic recording-reproducing apparatus provided with the head drumapparatus 1. When an operation command is entered to start recording orreproducing data, the rotating drum 11 of the head drum apparatus 1rotates. In addition, a pinch roller and a plurality of tape guides moveto wind the magnetic tape 2 around the head drum apparatus 1. A capstanand a take-up reel rotate to run the magnetic tape 2 and the operationof writing the signal or reading the recorded signal is performed.

FIG. 1 is a plan view showing a configuration example of the magneticreproducing head section 13. FIG. 3 is a side view showing aconfiguration example of the magnetic reproducing head section 13. FIG.1 shows an enlarged detail of a position for mounting the magneticreproducing head section 13 viewed from an arrow A in FIG. 2, i.e., froma bottom of the head drum apparatus 1. FIG. 3 shows the magneticreproducing head section 13 viewed from an arrow B in FIG. 1. Theconfiguration example of the magnetic reproducing head section 13 willnow be described with reference to FIGS. 1 and 3.

The magnetic reproducing head section 13 is structured to arrange an MRelement 13 c, and a pair of shielding films 13 d and 13 e made of a softmagnetic material between the head substrate 13 a and the protectivesubstrate 13 b that are electrostatic-discharge resistant conductive.Insulating films 13 f and 13 g are formed between the head substrate 13a and the protective substrate 13 b, and between the shielding films 13d and 13 e. The MR element 13 c is formed between the shielding films 13d and 13 e via insulating films 13 h and 13 i for sensing magnetism onthe magnetic tape 2.

In the magnetic reproducing head section 13, the shielding films 13 dand 13 e constitute a pair of magnetic shielding members. The MR element13 c is provided in a shield gap between the pair of magnetic shieldingmembers. This structure improves frequency characteristics andresolution. The shielding films 13 d and 13 e are made of, e.g.,Permalloy plated films. The insulating films 13 f through 13 i are madeof Ai₂O₃, for example. These films are formed on the head substrate 13 aaccording to the thin film technology. The protective substrate 13 b isjoined to form the magnetic reproducing head section 13. An edge surfaceof the magnetic reproducing head section 13 faces toward the outside(the bottom direction in FIG. 1) from the external surface of therotating drum 11. The edge surface is polished to function as a contactsurface with the magnetic tape 2.

The magnetic reproducing head section 13 is connected to terminals 15 aand 15 b through conducting wires 14 a and 14 b etc. to supply power tothe magnetic reproducing head section 13. Further, as shown in FIG. 3,the magnetic reproducing head section 13 is bonded to a conductive basemetal 16 by means of an epoxy adhesive 17, for example. The base metalis fixed to the rotating drum 11 through a conductive fixing screw 18.

The base metal 16 is made of, e.g., copper or the like. The base metal16 is fixed with the conductive fixing screw 18 and is electricallyconnected to the rotating drum 11. In addition to the adhesive 17, forexample, the conductive paste 19 or the like is used to electricallyconnect the head substrate 13 a and the protective substrate 13 b to thebase metal 16. For example, silver paste is used for the conductivepaste 19. The rotating drum 11 is formed of aluminum or the like and istherefore conductive. For example, a spring is connected to the rotatingdrum 11. The spring contacts with, e.g., a chassis used as a ground forthe magnetic recording-reproducing apparatus, providing a groundpotential. Accordingly, the head substrate 13 a and the protectivesubstrate 13 b are connected to the rotating drum 11 via the conductivepaste 19, the base metal 16, and the fixing screw 18, and is providedwith the ground potential.

FIGS. 1 and 3 show enlarged views of the MR element 13 c for easyunderstanding. Actually, however, the MR element 13 c is very smallcompared to the head substrate 13 a and the protective substrate 13 b.

Normally, a high-resistance synthetic resin material is used for acassette case to take up and store the magnetic tape 2. Such cassettecase is easily charged with electrostatic change during handling by auser, for example, when the cassette case is rubbed with a packagingmaterial or gloves made of artificial fiber or when the cassette case isrubbed against other parts during loading into the magneticrecording-reproducing apparatus. Accordingly, the electrostaticallycharged magnetic tape 2 may touch or approach the magnetic reproducinghead section 13.

The head drum apparatus 1 specifies the electrical resistivity of 10¹⁰Ωcm or less for the head substrate 13 a and the protective substrate 13b of the magnetic reproducing head section 13. As a result, the headsubstrate 13 a and the protective substrate 13 b are protected againstan electrostatic charge and are set to the ground potential. Thisprovides a flow of electric charge without a route to the MR element 13c when the magnetic tape 2 touches the magnetic reproducing head section13.

However, it is impossible to completely prevent a discharge to the MRelement 13 c from the touched or approaching magnetic tape 2. If too lowan electrical resistivity is given to the head substrate 13 a and theprotective substrate 13 b, the magnetic tape 2 or the MR element 13 capplies an excess discharge current to the head substrate 13 a or theprotective substrate 13 b. Consequently, the discharge current causesmeltdown for the MR element 13 c, the shielding films 13 d and 13 e, thehead substrate 13 a, and the protective substrate 13 b or dielectricbreakdown for the insulating films 13 f, 13 g, 13 h, and 13 i.

During a production line process of the head drum apparatus 1, forexample, a charged substance such as rubbed artificial fiber may touchor approach the terminals 15 a and 15 b and the conducting wires 14 aand 14 b. An electric charge moves from the charged substance toincrease the voltage of the MR element 13 c. One or more of theinsulating films 13 f through 13 i are subject to dielectric breakdown,allowing a discharge current to flow. If too low an electric resistanceis given to the head substrate 13 a or the protective substrate 13 b, anexcess current is applied to these substrates from the MR element 13 c.A discharged location is destroyed to generate a discharged trace.

The amount of discharge current must be regulated to prevent themagnetic reproducing head section 13 from being damaged due to an excessdischarge current during a discharge. For this reason, the head drumapparatus 1 according to the present invention uses anelectrostatic-discharge resistant conductive material for the headsubstrate 13 a and the protective substrate 13 b to prevent anelectrostatic charge and an excess discharge current from occurring.Specifically, the material to be used has the electrical resistivity of10² to 10¹⁰ Ωcm.

When a charged substance touches or approaches the terminals 15 a and 15b, for example, an electric field concentrates on, e.g., the shieldingfilm 13 d or the head substrate 13 a from the MR element 13 c at thecontact surface of the magnetic tape 2, generating a high voltage. Whenan electrostatic-discharge resistant conductive material is used for thehead substrate 13 a, the MR element 13 c generates a discharge currentof several to several tens of milliamperes to the shielding film 13 dand the head substrate 13 a. Consequently, no meltdown occurs at thesedischarged positions. The insulating films 13 f and 13 h are free fromdielectric breakdown.

The following describes in more detail the electrostatic-dischargeresistant conductive material available for the head substrate 13 a andthe protective substrate 13 b.

The electrostatic-discharge resistant conductive material available forthe present invention can be α-Fe₂O₃ (α-hematite). Generally, α-Fe₂O₃ ischaracterized by the electrical resistivity of 10⁵ to 10⁷ Ωcm. When thismaterial was actually used for the head substrate 13 a, for example,actual measurements showed the electrical resistivity of 7.7×10⁵ Ωcm or7.7×10⁶ Ωcm. The α-Fe₂O₃ material becomes nonmagnetic within the rangeof −10° to 60° C. as a normal operating temperature.

A more preferable electrostatic-discharge resistant conductive materialcan be a ferrite material that excels in the abrasion resistance to themagnetic tape 2. More specifically, available examples include NiZnferrite, Mnzn ferrite, etc. These ferrite materials are often used asmagnetic materials. To prevent an effect on magnetic characteristics ofthe MR element 13 c, the present invention requires the Curietemperature to be −10° C. (lower bound for the normal operatingtemperature) or lower.

The following composition ratios are applicable to the ferrite materialshaving the above-mentioned characteristics. The NiZn ferrite shouldcomprise 45 to 55 mol % of Fe₂O₃ and 38 to 50 mol % of ZnO with theremainder of NiO. In this case, NiO must be always contained. The MnZnferrite should comprise 48 to 55 mol % of Fe₂O₃ and 31 to 50 mol % ofZnO with the remainder of MnO. Also in this case, MnO must be alwayscontained.

Here are presented actual measurements for the manufactured MnZnferrites. The MnZn ferrite comprises 48 mol % of Fe₂O₃, 40 mol % of ZnO,and 12 mol % of MnO. Such MnZn ferrites are manufactured through thepressure and heat treatment in a reducing atmosphere and a normal oxygenatmosphere. Both MnZn ferrites showed the Curie temperature of −20° C.or lower and relative permeability μ of 1.5 at 20° C. The electricalresistivity resulted in 10³ Ωcm after the treatment in the reducingatmosphere and in 10⁷ Ωcm after the treatment in the normal atmosphere.

The above-mentioned electrostatic-discharge resistant conductivematerial is used for the head substrate 13 a and the protectivesubstrate 13 b. These substrates are set to the ground potential. Whenan electrostatically charged substance touches or approaches themagnetic reproducing head section 13, the substrates are protectedagainst being charged electrostatically. Further, it is possible todischarge a discharge current generated by electrostatic discharge fromthe charged substance by decreasing the discharge current to a safelevel. This can prevent an electrostatic discharge damage for the MRelement 13 c, the shielding films 13 d and 13 e, the head substrate 13a, the protective substrate 13 b, etc.

A chance of causing an electrostatic discharge damage decreases when acharged substance exists near the magnetic reproducing head section 13during a production line process of the head drum apparatus 1. As aresult, the yield ratio improves. Further, the electrostatic dischargedecreases even if it occurs duet to a contact between the magneticreproducing head section 13 and the magnetic tape 2. This prevents anelectrostatic discharge damage to the MR element 13 c due to frictionwith the magnetic tape 2. Even if the surface of the magnetic tape 2 iscoated with a high-resistance magnetic film that can be easily chargedwith electrostatic change, the MR element 13 c becomes less frequentlysubject to an electrostatic discharge damage.

The above-mentioned magnetic reproducing head section 13 uses theelectrostatic-discharge resistant conductive material for both the headsubstrate 13 a and the protective substrate 13 b. Theelectrostatic-discharge resistant conductive material may be used toform only either of these substrates.

The above-mentioned head drum apparatus 1 can be used for not onlymagnetic recording-reproducing apparatuses, but also magneticreproducing apparatuses only capable of magnetic tape reproduction.

The foregoing invention has been described in terms of preferredembodiments. However, those skilled, in the art will recognize that manyvariations of such embodiments exist. Such variations are intended to bewithin the scope of the present invention and the appended claims.

1. A magnetic reproducing head to read a recording signal in contactwith magnetic tape, comprising: a base metal; and a magnetic headsection fixed to the base metal, wherein a magnetoresistive effectelement is used for a head element section comprising first and secondinsulating films provided between a pair of magnetic shielding films;the head element section is structured to be provided between a headsubstrate and a protective substrate electrically connected to the basemetal via third and fourth insulating films; and at least one of thehead substrate and the protective substrate are formed of a materialcomprising one of an NiZn ferrite and an MnZn ferrite with an electricalresistivity of 10² to 10⁷ Ωcm and a Curie temperature of lower than −10°C.
 2. The magnetic reproducing head according to claim 1, wherein theNiZn ferrite comprises 45 to 55 mol % of Fe₂O₃, 38 to 50 mol % of ZnO,and remaining more than 0 mol % of NiO.
 3. The magnetic reproducing headaccording to claim 1, wherein the MnZn ferrite comprises 48 to 55 mol %of Fe₂O₃, 31 to 50 mol % of ZnO, and remaining more than 0 mol % of MnO.4. A head drum apparatus to write or read a signal on or from magnetictape, comprising: a rotating drum having conductivity to be a groundpotential, wherein the magnetic tape is helically wound around anexternal surface of the rotating drum; a base metal which is fixedinside the rotating drum and is electrically connected to the rotatingdrum; and a magnetic head section fixed to the base metal, wherein amagnetoresistive effect element to read a recording signal in contactwith the magnetic tape is used for a head element section comprisingfirst and second insulating films provided between a pair of magneticshielding films; the head element section is structured to be providedbetween a head substrate and a protective substrate electricallyconnected to the base metal via third and fourth insulating films; andat least one of the head substrate and the protective substrate areformed of a material comprising one of an NiZn ferrite and an MnZnferrite with an electrical resistivity of 10² to 10⁷ Ωcm and a Curietemperature of lower than −10° C.
 5. The head drum apparatus accordingto claim 4, wherein the NiZn ferrite comprises 45 to 55 mol % of Fe₂O₃,38 to 50 mol % of ZnO, and remaining more than 0 mol % of NiO.
 6. Thehead drum apparatus according to claim 4, wherein the MnZn ferritecomprises 48 to 55 mol % of Fe₂O₃, 31 to 50 mol % of ZnO, and remainingmore than 0 mol % of MnO.
 7. A magnetic recording-reproducing apparatusto record and reproduce a signal using magnetic tape, comprising: arotating drum having conductivity to be a ground potential, wherein themagnetic tape is helically wound around an external surface of therotating drum; a base metal which is fixed inside the rotating drum andis electrically connected to the rotating drum; and a magnetic headsection fixed to the base metal, wherein a magnetoresistive effectelement to read a recording signal in contact with the magnetic tape isused for a head element section comprising first and second insulatingfilms provided between a pair of magnetic shielding films; the headelement section is structured to be provided between a head substrateand a protective substrate electrically connected to the base metal viathird and fourth insulating films; and at least one of the headsubstrate and the protective substrate are formed of a materialcomprising one of an NiZn ferrite and an MnZn ferrite with an electricalresistivity of 10² to 10⁷ Ωcm and a Curie temperature of lower than −10°C.
 8. The magnetic recording-reproducing apparatus according to claim 7,wherein the NiZn ferrite comprises 45 to 55 mol % of Fe₂O₃, 38 to 50 mol% of ZnO, and remaining more than 0 mol % of NiO.
 9. The magneticrecording-reproducing apparatus according to claim 7, wherein the MnZnferrite comprises 48 to 55 mol % of Fe₂O₃, 31 to 50 mol % of ZnO, andremaining more than 0 mol % of MnO.